Internal combustion engines can experience increased emissions during cold starts. Since the catalyst is not lit off, engine raw emissions may not be sufficiently converted by the catalytic converter. Some attempts to reduce the amount of raw emission introduction into the atmosphere during cold starts include loading catalytic converters with relatively large amounts of precious metals, or providing alternative cold start strategies that may be integrated in the engine control unit (ECU).
One such cold start strategy is disclosed in U.S. Pat. No. 5,497,619, wherein an exhaust passage connecting an exhaust manifold to an exhaust pipe bends at 90 degrees. A catalyst unit is on the exhaust passage located downstream from the bend. An HC adsorbent is provided in an extended portion near the bend, in a straight traveling direction from the exhaust manifold. The HC adsorbent is arranged to trap hydrocarbons discharged from the exhaust manifold at startup by being brought into collision with the HC adsorbent by inertia. An EGR pipe is connected downstream from the HC adsorbent. The EGR pipe is connected to an intake manifold via an EGR control valve. When the operation condition of the engine satisfies an EGR condition similar to a conventional case, the EGR control valve is opened, and the intake manifold and HC adsorbent communicate with each other. As a result, part of the exhaust gas begins to flow through the HC adsorbent, causing the HC adsorbent to be heated by the heat of the exhaust gas, and desorption of the HC trapped in the adsorbent begins.
The inventors herein have recognized several issues with this approach. As one example, only until the engine satisfies the EGR flow enabling condition does the exhaust flow through the HC trap. Prior to then the exhaust flow is directed through the catalyst, to the atmosphere, while the catalyst is still too cold to be effective. The amount of absorption of the hydrocarbons by the HC adsorbent is limited by the amount of interaction the exhaust gas makes with the adsorbent as it rounds the bend on its way to the catalyst, which can be relatively low especially for initial combustion events.
In order to at least partially address these shortcomings, methods and systems are provided for managing exhaust gases from an internal combustion engine. One example exhaust system may include an EGR line configured to route a selected amount of exhaust gases from an exhaust passage of the engine toward an intake passage of the engine. A gas component reduction element may be located in the EGR line, and may be configured to reduce a quantity of one or more selected components from the selected amount of exhaust gases. A treated exhaust line may be coupled with the EGR line, and may be configured to route a first portion of the selected amount of the exhaust gases from the gas component reduction element to pass into the intake passage of the engine, and to allow a second portion of the selected amount of the exhaust gases to the atmosphere.
In this way, increased exhaust gases may pass through the gas component reduction element before passing to the atmosphere while the catalyst is still cold where selected components, such as hydrocarbons, may be absorbed. Also in this way, the engine performance may be kept within a predetermined range by selectively allowing only the first portion to pass into the intake passage, and allowing for EGR ratio control during the initial engine starting.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.